This invention relates to new, nitrogen-containing, low-viscosity polyester polyols, a process for their production and their use in the production of polyurethane (urea)s and polyisocyanurates.
Rigid foams produced by the isocyanate polyaddition process have now become a significant class of materials in the field of insulation. In general, such foams are rigid polyurethane (urea) foams and, in particular, rigid polyisocyanurate foams. The latter foams show high flame resistance on their own without the assistance of additives. Rigid foams are generally produced from polyisocyanates and polyether polyols or from a mixture of polyether and polyester polyols. Combinations of various polyol components with additives are generally used in cases where the rigid foams have to satisfy certain flameproofing standards.
The advantage of polyether polyols is that predetermined functionalities may be adjusted as required through the starter species (polyols or polyamines). Polyols specific to rigid foams, for example polyols based on sorbitol or sucrose starters having a functionality of greater than 4 and also a low viscosity, may be produced from polyethers and have OH numbers in the range of from 200 to 600.
In order to reach certain flameproofing standards, polyester polyols, generally of high viscosity, are added to the starting polyethers. However, on account of their lower functionality, the polyester polyols may only be added in limited quantities because otherwise the resulting foam would be too flexible. Other components used in the production of flame resistant polyurethane foams are phosphoric or phosphonic acid esters or other phosphorus derivatives which, for the most part, cannot be incorporated, i.e. are able to migrate and likewise to soften the foam. Of greater advantage in regard to migration are the incorporable phosphonic acid esters, such as Baytherm.RTM. 4090 N (a product of Bayer AG, Leverkusen). Unfortunately, phosphonic acid esters also have a softening effect due to their bifunctionality and may only be added in limited quantities. Halogen-based flameproofing agents often have a similar effect and in addition, give off corrosive gases, particularly during the burning of foams.
It would therefore be particularly advantageous to have rigid foam polyols which satisfy the following criteria:
(a) increased functionality by comparison with standard polyester polyols in order to be able to dispense with the copolyethers of relatively high functionality hitherto necessary; PA1 (b) low viscosity in polyester polyols of relatively high functionality; PA1 (c) inherent flameproofing properties which eliminate or reduce the need to use non-incorporable, flexibilizing flameproofing agents which give off corrosive gases in the event of fire and PA1 (d) production of rigid foams with high thermal stability and high mechanical strength.